Crystal oscillators are used for a variety of analog and digital electronic products such as microprocessors, microcontrollers, radio transmitters and receivers, and the like. Crystal oscillators use the resonance characteristics of quartz crystals to provide references for the generation of very accurate clock frequencies. Crystal oscillator circuits generally use tank capacitors connected to crystal terminals with a negative gain element between them to start and maintain oscillation at the desired frequency. In simple crystal oscillator circuits, an inverter provides the negative loop gain. Other crystal oscillator circuits use variable loop gain elements and gain control circuits to establish a gain that is sufficient to start oscillations but also low enough to avoid excessive power consumption during steady state operation. However because crystal oscillators consume significant amounts of power, it would be desirable to reduce power consumption further, especially for very low power products that use batteries.
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.